The present invention relates to an electromagnetic shielding plate and a method for producing the same
An electromagnetic shielding plate is used, for example, as a front filter to be attached to a display, since it can shield electromagnetic waves leaking from the display. The electromagnetic shielding plate used as the front filter should have a property not to decrease the visibility of a display screen of the display in addition to the property to shield the electromagnetic waves. As such an electromagnetic shielding plate, a shielding plate comprising a transparent substrate and a conductive mesh attached to the substrate is known. The conductive mesh is a mesh of conductive fibers knit in a lattice form, and a conductive fiber comprising organic fiber (e.g. polyester fiber, etc.) having a metal thin layer formed on the surface thereof is used.
However, the electromagnetic shielding plate comprising the conductive mesh has a problem that the handling of the mesh is not easy, since the conductive mesh, which is a knit, easily expands and contracts when the plate is produced. Furthermore, the transmittance of visible light of the electromagnetic shielding plate should be increased so that the electromagnetic shielding plate is used as the front filter of the display. To this end, the lattice distance of the conductive mesh is enlarged and also the fiber diameter should be decreased. Such a conductive mesh more easily expands and contracts, so that the handling thereof becomes more difficult. In addition, such a conductive mesh, which easily expands and contracts, has a problem that it tends to suffer from the change of the lattice distance and the deformation of the lattice pattern, when it is adhered to the transparent substrate.
To solve the above problems, it is proposed to adhere an etched sheet of a metal foil, which is etched in a lattice form, to the surface of a transparent substrate. However, when a front filter to be attached to a display having a large area such as a plasma display or a large-size cathode-ray tube (CRT) is produced, a metal foil having a large area comparable to the area of the display should be etched in the lattice form. To etch such a large metal film, a large-scale lithographic process is necessary. Thus, such an electromagnetic shielding plate may not be easily produced.
JP-A-62-57297 and JP-A-02-52499 disclose an electromagnetic shielding plate formed by printing a conductive paint in the form of a lattice or stripes. The electromagnetic shielding plate disclosed in these JP-A publications has a lattice distance of about 1,000 xcexcm and a line width of about 100 xcexcm. Thus, it does not have sufficient electromagnetic shielding properties. In addition, the lattice lines tend to be observable and the visibility of the display may be decreased. Furthermore, the adhesion of the lattice formed from such a conductive paint to a glass substrate is insufficient.
JP-2000-13088A discloses a method for forming a geometric pattern with thin lines on a film using a printing process which allows the printing of a highly fine pattern. However, when such a film is attached to a display as an electromagnetic shielding filter, a step to adhere such a film to a self-supporting plate is necessary in addition to a step to impart low reflection properties and near infrared ray-shielding properties to the film. As a result, the number of steps for the production of the filter increases. In addition, defects such as creasing may appear in handing. Therefore, the handling manner should be reformed. Accordingly, this method needs further improvements. Furthermore, when the geometric pattern is formed on the glass substrate with the currently used paste, the adhesion of the pattern to the substrate is insufficient.
EP-A-0 998 182 discloses an electromagnetic shielding plate on which a fine geometric pattern is formed with a printing method. The adhesion of such a geometric pattern to the glass substrate is also insufficient.
JP-A-10-64435 and JP-2001-6435A disclose the addition of glass powder to a paste, which is used to form an internal electrode of a plasma display panel, but they do not disclose the use of glass powder in an electromagnetic shielding plate which requires high visibility and good electromagnetic shielding properties.
The electromagnetic shielding plate is often required to have high shielding properties, when it is used as the front filter of the plasma display panel. In such a case, a metal thin layer is formed on the surface of a pattern by wet plating to increase the conductivity, and thus it is desired to form a pattern which has good plating properties and withstands wet plating. When the electromagnetic shielding plate is used as the front filter of the plasma display panel, it is also desired for the plate to physically protect a module, and to prevent the scattering of fragments, if the module is broken.
An object of the present invention is to provide an electromagnetic shielding plate comprising a glass substrate and a geometric pattern formed on the substrate, in which the adhesion of the pattern to the glass substrate is good, an additional metal layer can be easily formed on the pattern by wet plating, the pattern is not stripped by the wet plating, and the visibility and strength of the plate is high.
To achieve the above object, the present invention provides an electromagnetic shielding plate comprising a glass substrate, a geometric pattern formed on the substrate and optionally a conductive metal layer formed on the geometric pattern, wherein said geometric pattern comprises (a) an inorganic filler selected from the group consisting of metals and metal oxides, and (b) a glass component having a softening point of about 200 to 700xc2x0 C.
In addition, the present invention provides a method for producing the electromagnetic shielding plate of the present invention comprising the steps of forming a geometric pattern by printing the pattern with a paste containing an inorganic filler selected from the group consisting of metal powder, metal alloy powder, metal oxide powder, organic metal complexes and organic acid salts of platinum metals, a glass frit, a binder resin and an organic solvent, baking the pattern until the weight of the organic material in the pattern is decreased to 10% or less of the weight of the organic material prior to baking, and optionally forming a conductive metal layer on the geometric pattern by wet plating.
The present invention has been completed based on the finding that an electromagnetic shielding plate having good electromagnetic shielding properties and also high visibility and strength can be easily produced, even if it has a large size, when a geometric pattern is formed on a glass substrate by printing the pattern with a paste containing an inorganic filler selected from the group consisting of metals and metal oxides and a glass frit having a softening point of about 200 to 700xc2x0 C., baking the pattern, and optionally forming a metal layer on the geometric pattern by wet plating.